As a method for supporting mobility of a terminal in a mobile communication system, there are a process called handover when the terminal is in an active mode and a cell reselection when the terminal is in an idle mode. The handover in the active mode is a method for supporting the mobility during communication, and the cell reselection is a method for supporting quick connection when communication is resumed from the idle mode.
While a cell reselection process used in a related-art 3GPP system considers only the same transmission mode, it has been modified into a cell reselection process in 3rd Generation Partnership Project Long Term Evolution (3GPP LTE), which allows to select cells of systems using different transmission modes.
The 3GPP cell reselection process is described in the 3GPP TS 36.304 “Evolved Universal Terrestrial Radio Access (E-UTRA) User Equipment (UE) procedures in idle mode (Release 8)”.
Parameters used in 3GPP LTE to apply the cell reselection process are as follows.                ThreshX-High: high threshold value applied to the same frequency and the same Radio Access Technology (RAT)        SintraSearch: threshold value starting the search of the same frequency and the same RAT cell        ThreshX-Low: low threshold value applied to the same frequency and the same RAT        SnonintraSearch: threshold value starting the search of different frequency and different RAT cell        ThreshServingLow: threshold value allowing to change the serving cell regardless of the priority when there is a cell satisfying a movement criteria        
3GPP LTE describes that the above parameters are provided and set by a system. A general relation between the above parameters is as follows.ThreshX-High>SintraSearch>ThreshX-Low>SnonintraSearch>ThreshServingLow 
The cell reselection process using these parameters is summarized as follows.
1. When the received signal strength of the serving cell has a value lower than SintraSearch, signal measurements are obtained on cells of the same frequency of the same RAT.
2. When the received signal strength of the serving becomes lower than SnonintraSearch, signal measurements are obtained on cells of the same RAT and different frequency and cells of different RAT. If there is a cell maintaining a value higher than the threshold value ThreshX-High for a certain time among cells having high priorities, then the cell is reselected.
3. When the received signal strength becomes lower than the threshold value ThreshServingLow, which means that the terminal cannot be connected to the current cell any longer, the terminal immediately moves to a possible cell that satisfies a reselection criteria.
The foregoing cell reselection process provides a cell reselection between various communication systems including terrestrial communication systems as well as 3GPP LTE. However, the process does not consider the characteristics of the satellite communication system. Thus, it results inefficiency in a communication system having both terrestrial communication system and satellite communication system.